The M-4 Sherman Medium Tank was the mainstay of American armored forces during World War II and the Korean War. It saw service on every front: North Africa, northern Europe, the eastern front, and the Pacific campaigns.

Except for the Soviet T-34, the M-4 Sherman probably had a greater effect on the course of the war than any other tank, light, medium, or heavy.

One day after the M-3 Medium Tank -- always considered an interim model -- was ordered into production, design work started on a new medium tank to overcome the deficiencies of the M-3. The main differences lay in increased armor protection and a new turret of conventional design that allowed the main gun to traverse 360°.

Its design number was T-6, and it was accepted for production in September 1941 as the M-4 Medium Tank. When Germany invaded Russia in June 1941, President Roosevelt personally ordered tank production for 1942 doubled from 1,000 to 2,000 per month. As a result, 11 separate companies manufactured the M-4 in an amazing example of management and quality control skills.

The M-4 design used as much of the M-3's suspension, chassis, and power plant as possible. The new turret was a one piece, 3-inch-thick casting, rounded to maximize protection from enemy gunnery. The turret was also motor driven. The M-4's upper hull was cast in separate parts and welded together.

This cutaway of the M-4 Sherman shows the cramped and dangerous conditions in which tank crews operated during World War II.

The M2 75mm 31.5 caliber main gun was gyrostabilized and had a muzzle velocity of 1,850 feet per second, considered too low even then. The M3 main gun was approved in June 1941 but only reached the European theater in time to have a decisive effect during the Ardennes Offensive in December 1944. The M3 gun had a longer barrel than the M2 and produced a muzzle velocity of 2,030 feet per second.

Starting in August 1942, work on a new 76mm gun wavered until finally, in early 1943, the Armor Board approved its installation on new M-4s. In late 1942 tests were conducted on an M-4 armed with a 105mm howitzer. The tests proved so successful that more than 4,600 105mm armed M-4s were built.

The M-4's armor was the thickest that had ever been applied to an American tank until that time. It ranged from 3 inches on the turret front to a little less than 2 inches on the hull front to .25 inch on the top of the hull.

Armor was later supplemented by appliqué armor. Tank crews found dozens of ingenious ways to supplement the M-4's armor with chunks of timber, additional steel plates, and elaborate racks and fences holding sandbags.

See the next page to read about the M-4 Sherman Medium Tank service and modification.